• Energy Research

Abstract The transition to renewable energy sources is pivotal in addressing global climate change challenges, with rooftop solar photovoltaic (PV) systems playing a crucial role. For informed decision-making in energy policy, it is important to have a comprehensive understanding of both the economic and environmental performance of rooftop solar PV. This study provides a high-resolution analysis of existing rooftop solar PV systems in Switzerland by assessing the robustness of the potential estimation to properly derive the amount of electricity generated by individual systems, and subsequently quantify the levelized cost of electricity and life cycle greenhouse gas (GHG) emissions of electricity generation from PV and compare them with those of grid electricity supplies. Our results indicate substantial geographical variations between potential estimations and real-world installations, with notable underestimations of approximately 1.3 Gigawatt-peak, primarily for systems around 10 kWp in size, mainly due to the quality of input data and conservative estimation. The study finds that in many regions and for most of the installed capacity, electricity generated from rooftop PV systems is more economical than the grid electricity supply, mainly driven by factors including high electricity prices, larger installations and abundant solar irradiance. The GHG emissions assessment further emphasizes the importance of methodological choice, with stark contrasts between electricity certificate-based approaches and others that are based on the consumption mix. This study suggests the need for more accurate geographical potential estimations, enhanced support for small-scale rooftop PV systems, and more incentives to maximize the potential of their roof area for PV deployment. As Switzerland progresses towards its renewable energy goals, our research underscores the importance of informed policymaking based on a retrospective analysis of existing installations, essential for maximizing the potential and benefits of rooftop solar PV systems.

Abstract The transition to renewable energy sources is pivotal in addressing global climate change challenges, with rooftop solar photovoltaic (PV) systems playing a crucial role. For informed decision-making in energy policy, it is important to have a comprehensive understanding of both the economic and environmental performance of rooftop solar PV. This study provides a high-resolution analysis of existing rooftop solar PV systems in Switzerland by assessing the robustness of the potential estimation to properly derive the amount of electricity generated by individual systems, and subsequently quantify the levelized cost of electricity and life cycle greenhouse gas (GHG) emissions of electricity generation from PV and compare them with those of grid electricity supplies. Our results indicate substantial geographical variations between potential estimations and real-world installations, with notable underestimations of approximately 1.3 Gigawatt-peak, primarily for systems around 10 kWp in size, mainly due to the quality of input data and conservative estimation. The study finds that in many regions and for most of the installed capacity, electricity generated from rooftop PV systems is more economical than the grid electricity supply, mainly driven by factors including high electricity prices, larger installations and abundant solar irradiance. The GHG emissions assessment further emphasizes the importance of methodological choice, with stark contrasts between electricity certificate-based approaches and others that are based on the consumption mix. This study suggests the need for more accurate geographical potential estimations, enhanced support for small-scale rooftop PV systems, and more incentives to maximize the potential of their roof area for PV deployment. As Switzerland progresses towards its renewable energy goals, our research underscores the importance of informed policymaking based on a retrospective analysis of existing installations, essential for maximizing the potential and benefits of rooftop solar PV systems.

Solar photovoltaics (PV) will play an important role in decarbonising the energy system. To date, most assessments of PV transition pathways focus on least-cost aspects, without neither considering the time needed to achieve a substantial PV deployment, nor the impacts on regional electricity supply equality. In this work, we propose two alternative PV expansion strategies for Switzerland: The first strategy prioritises the most pro-ductive roofs and reaches national PV targets by exploiting the minimum number of rooftops, while the second strategy aims at maximising regional self-sufficiency as proxy of PV supply equality. Both strategies are assessed for several PV expansion scenarios using real hourly PV potential data for the entire Swiss building stock. The scenarios are compared to hourly electricity demand profiles for the residential and service sector. Results suggest that when employing the first strategy, at least 46% of suitable rooftops - mostly large roofs with low tilt angles - are needed to reach Switzerland's 2050 PV expansion target of 35 TWh. For the projected electricity demand in 2050, this leads to annual electricity self-sufficiency in about 40% of Swiss districts. This percentage can be increased to over 70% by following strategy two to maximise self-sufficiency - which may feature sev-eral economic and societal advantages - at the cost of covering 86% of suitable rooftops with PV. The findings may support policy makers and local utilities to find efficient and equitable pathways for a decentralised PV expansion, while at the same time reaching the ambitious national renewable energy targets within due time.

Solar photovoltaics (PV) will play an important role in decarbonising the energy system. To date, most assessments of PV transition pathways focus on least-cost aspects, without neither considering the time needed to achieve a substantial PV deployment, nor the impacts on regional electricity supply equality. In this work, we propose two alternative PV expansion strategies for Switzerland: The first strategy prioritises the most pro-ductive roofs and reaches national PV targets by exploiting the minimum number of rooftops, while the second strategy aims at maximising regional self-sufficiency as proxy of PV supply equality. Both strategies are assessed for several PV expansion scenarios using real hourly PV potential data for the entire Swiss building stock. The scenarios are compared to hourly electricity demand profiles for the residential and service sector. Results suggest that when employing the first strategy, at least 46% of suitable rooftops - mostly large roofs with low tilt angles - are needed to reach Switzerland's 2050 PV expansion target of 35 TWh. For the projected electricity demand in 2050, this leads to annual electricity self-sufficiency in about 40% of Swiss districts. This percentage can be increased to over 70% by following strategy two to maximise self-sufficiency - which may feature sev-eral economic and societal advantages - at the cost of covering 86% of suitable rooftops with PV. The findings may support policy makers and local utilities to find efficient and equitable pathways for a decentralised PV expansion, while at the same time reaching the ambitious national renewable energy targets within due time.

Abstract The extraction of shallow geothermal energy using borehole heat exchangers (BHEs) is a promising approach for decarbonisation of the heating sector. However, a dense deployment of BHEs may lead to thermal interference between neighboring boreholes and thereby to over-exploitation of the heat capacity of the ground. Here we propose a novel method to estimate the technical potential of BHEs which takes into account potential thermal interference as well as the available area for BHE installations. The method combines simulation of the long-term heat extraction through BHEs for a range of borehole spacings and depths and includes an optimisation step to maximise the heat extraction. Application of the method to a case study in western Switzerland, from an available area of 284 km 2 , yields an annual technical potential of 4.65 TWh and a maximum energy density of 15.5 kWh / m 2 . The results also suggest that, for a minimum borehole spacing of 5 m and a maximum borehole depth of 200 m , the cumulative installed borehole depth should not exceed 2 km / ha . The estimated technical potential can be used by urban planners for the techno-economic analysis of BHE systems and by policy makers to develop strategies that encourage the use of shallow geothermal energy.

Abstract The extraction of shallow geothermal energy using borehole heat exchangers (BHEs) is a promising approach for decarbonisation of the heating sector. However, a dense deployment of BHEs may lead to thermal interference between neighboring boreholes and thereby to over-exploitation of the heat capacity of the ground. Here we propose a novel method to estimate the technical potential of BHEs which takes into account potential thermal interference as well as the available area for BHE installations. The method combines simulation of the long-term heat extraction through BHEs for a range of borehole spacings and depths and includes an optimisation step to maximise the heat extraction. Application of the method to a case study in western Switzerland, from an available area of 284 km 2 , yields an annual technical potential of 4.65 TWh and a maximum energy density of 15.5 kWh / m 2 . The results also suggest that, for a minimum borehole spacing of 5 m and a maximum borehole depth of 200 m , the cumulative installed borehole depth should not exceed 2 km / ha . The estimated technical potential can be used by urban planners for the techno-economic analysis of BHE systems and by policy makers to develop strategies that encourage the use of shallow geothermal energy.

This dataset contains an estimation of the useful and technical potential of shallow ground-source heat pumps (GSHPs) for Western Switzerland, at a spatial resolution of 400 x 400 m2. The technical potential is hereby defined as the maximum energy that could be extracted from GSHP systems in case of their dense deployment, such as to avoid the over-exploitation of the heat capacity of the ground. We consider GSHPs with vertical closed-loop borehole heat exchangers (BHE) installed at depths of 50 - 200 m. The useful potential is defined as the potential that could be delivered to building heating and cooling systems via a water-to-water heat pump. The datasets contains future scenarios of heating and cooling demand, space cooling equipment deployment (service sector only) and climate change models and considers the potential use of DHC. The dataset covers around 80,000 property units (parcels) in the Swiss Cantons of Vaud and Geneva, excluding only the areas of the Alps and the Jura mountains. The data package contains information on the available area for GSHP systems, the heating and cooling demand as well as the resulting technical and useful potentials for all simulated scenarios of future cooling demand (200 Monte Carlo runs), for the case of direct heat supply (per pixel of 400 x 400 m2) as well as for district heating and cooling (DHC). In scenarios without DHC (direct heat supply), the results are summarized by pixel of 400 x 400 m2. In scenarios with DHC, the results of potentials within DHCs are summarized by DHC (see *_in_dhc.csv) while potentials outside of DHCs are summarized by pixel (see *_outside_dhc.csv). For details on the methodology applied to obtain the results provided in the data package, please refer to the above-mentioned research articles. A description of all files is provided in Dataset documentation.pdf and metadata is provided in Datapackage.json.

This dataset contains an estimation of the useful and technical potential of shallow ground-source heat pumps (GSHPs) for Western Switzerland, at a spatial resolution of 400 x 400 m2. The technical potential is hereby defined as the maximum energy that could be extracted from GSHP systems in case of their dense deployment, such as to avoid the over-exploitation of the heat capacity of the ground. We consider GSHPs with vertical closed-loop borehole heat exchangers (BHE) installed at depths of 50 - 200 m. The useful potential is defined as the potential that could be delivered to building heating and cooling systems via a water-to-water heat pump. The datasets contains future scenarios of heating and cooling demand, space cooling equipment deployment (service sector only) and climate change models and considers the potential use of DHC. The dataset covers around 80,000 property units (parcels) in the Swiss Cantons of Vaud and Geneva, excluding only the areas of the Alps and the Jura mountains. The data package contains information on the available area for GSHP systems, the heating and cooling demand as well as the resulting technical and useful potentials for all simulated scenarios of future cooling demand (200 Monte Carlo runs), for the case of direct heat supply (per pixel of 400 x 400 m2) as well as for district heating and cooling (DHC). In scenarios without DHC (direct heat supply), the results are summarized by pixel of 400 x 400 m2. In scenarios with DHC, the results of potentials within DHCs are summarized by DHC (see *_in_dhc.csv) while potentials outside of DHCs are summarized by pixel (see *_outside_dhc.csv). For details on the methodology applied to obtain the results provided in the data package, please refer to the above-mentioned research articles. A description of all files is provided in Dataset documentation.pdf and metadata is provided in Datapackage.json.